TORONTO — An attempted cyber-attack on the NDP's electronic voting system Saturday forced party officials to delay the process of choosing the next federal New Democrat leader for several hours, frustrating voters both at the convention in Toronto and across the country.

Party officials insisted the integrity of the voting system was not compromised, but acknowledged that the would-be hacker managed to "mess'' it up enough to cause lengthy delays.

He stopped short of suggesting someone was deliberately trying to sabotage the NDP leadership process.

"I'm saying that somebody outside of the party was attempting to mess with our one-member, one-vote (system), but that the sanctity of our system was preserved because of the failsafes,'' Lavigne said.

He said he was told "they did isolate it to two — or it may have been three — IP addresses, but they've resolved it.''

Party president Rebecca Blaikie insisted that while the attempted attack proved a nuisance to the party and its voters, it did not penetrate the system nor compromise the voting results.

"Whoever this is or whatever it came from, their goal was simply to make it a pain to get into our site, to make it harder for people to vote, to block it up with a lot of traffic,'' Blaikie said.

"But traffic has nothing to do with security and so the vote itself is fine. It's just meant that we've had to have a lot more patience today than we thought.''

Earlier, officials would say only that the system had been overwhelmed due to an unanticipated crush of voters all trying to cast their online ballots at the same time.

But that explanation was met with skepticism, since fewer than 10,000 New Democrats actually voted electronically on Saturday; the vast majority, some 56,000, had cast their ballots in advance.

The party hired Scytl, a Spanish-based company that specializes in electronic voting security, to run the online voting system.

Results from the second round of voting were delayed about two hours to give every member who wanted to vote a chance to do so.

For those who voted in person at the convention, lengthy lineups at voting stations formed as the delays pushed balloting well into the afternoon.

When third ballot results were finally announced, front-runner Thomas Mulcair had edged closer to victory, taking 43.8 per cent of the vote to Brian Topp's 31.6. Nathan Cullen came third with 24.6 per cent of the votes and was knocked off the ballot.

Peggy Nash, Paul Dewar, Martin Singh and Niki Ashton were all knocked out of the race during first- and second-ballot voting.